Abstract
TiAlN/SiN x multilayers were fabricated by a reactive magnetron sputtering system combining r.f. and d.c. power sources. The SiN x layer thickness (l SiNx ) was 0.4 and 1 nm, while the layer thickness ratios (l TiAlN /l SiNx ) of TiAlN to SiN x were adjusted to be 4/0.4 and 4/1, respectively. Characterizations by XRD, TEM, SEM and nano-indentation revealed the dependence of l SiNx on the preferred orientation, crystalline behavior, microstructure and hardness. The crystalline SiN x grew epitaxially and formed the coherent interfaces with the TiAlN, exhibiting the maximum hardness of 42 GPa. However, SiN x evidently transformed from crystalline to amorphous when the l SiNx increased to 1 nm, while microstructure of films changed from columnar feature to more densified one. The corrosion resistance of coatings in 3.5 wt % NaCl aqueous solution was investigated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The denser microstructure exhibited the lower corrosion rate and higher polarization impedance. It was revealed that the amorphous SiN x altered the coherent interfaces and the superlattice structure, leading to the improved anti-corrosion performances.